MRSA
Staphylococcus aureus is known to inhabit the nasal cavities of 30% of the population [3 . Under some conditions, the microorganism can become pathogenic and cause issues such as skin infections. A widespread problem has been the emergence of Staphylococcus aureus that is resistant to certain antibiotics. Methicillin-resistant Staphylococcus aureus (MRSA) was first isolated in the 1960s. The bacterium has two types: community-acquired MRSA, and hospital-acquired MRSA [4]. The resistant bacterium in hospitals is particularly a concern due to life-threatening circumstances for immunocompromised patients. Emergence of resistance MRSA’s lineage originated from methicillin-susceptible Staphylococcus aureus by acquiring Staphylococcal cassette chromosome mec (SCC''mec'') [4 ]. One particular clone, ST239, is a bacterial hybrid of a complex of two clones, with ST30 and ST8 as the founders of this complex. This ST239 MRSA clone also seems to be found in hospital cases around the world over the years. SCC''mec'' is a genomic island which encompasses horizontal gene transfer. The determinant for methicillin resistance is contained within the Staphylococcal chromosome cassette mec. Incorporation of SCCmec into the chromosome of Staphylococcus aureus occurs in the SCC''mec'' attachment site locus (attB) [2]. This attachment site is found towards the end of the open reading frame orfX. SCC''mec'' is an element of genetic variability, within which lies the methicillin resistance determinant, mecA, as well as recombinase genes ccrAB and ccrC [2]. β-lactam antibiotics target either transpeptidases or penicillin-binding proteins (PBPs) that are essential for the makeup of bacterial cell walls. In MRSA,'' mec''A has an alternative form of a penicillin-binding protein, PBP2a, which is less effected by β-lactam antibiotics. Because of this, MRSA culture’s cell walls can stay intact. TW20: a highly resistant clone The first case of ST239 mRSA was described in 1992 in Brazil. By using multilocus sequence typing, TW20 was determined to be a sequence type 239 (ST239). TW20 has been isolated and described in many studies, one of which is described below. TW20 was first isolated in October of 2003. The strain was worrisome due to its enhanced resistance to a great number of antibiotic drugs, including: tetracycline, methicillin, penicillin, ciprofloxacin, gentamicin, erythromycin, neomycin, and trimethoprim (Holden et al). The genome of TW20 was sequenced an annotated. This genome is contained within a single chromosome that has 3,043,210 base pairs. This chromosome is depicted in Figure 1. This has been notably the largest genome of'' Staphylococcus aureus'' that has ever been sequenced. In Figure 1, the SCC element that has been described in this article is shown in yellow. The red regions are the genomic islands that have also been described previously, in which DNA was obtained through horizontal gene transfer. Genomes were compared with other strains in a study conducted by Holden et al., and these researchers found that the highest matches were with MRSA 252 (also known as ST36), a dominant clone found in hospitals in the United Kingdom. Strain 16K, a variant of ST239 In a study conducted by Yamamoto et al., researchers isolated MRSA from Russian patients in hospitals, as well as patients in the community with nongonococcal urethritis. Stain 16K, a variant of ST239, was isolated. D rug resistance evolution was investigated with the reference of TW20. This analysis is shown in Figure 2. Contigs were obtained through pyrosequencing, followed by mapping onto the TW20 genome. Information on the 16K genome is written outside the circles, while TW20 information is found inside the circles. Green areas indicate that the genomes have high homology. Yellow indicates that 16K is less or non-homologous to TW20, while blue signifies divergence from TW20 (Yamamoto et al., 2012). References [1 Holden M, Lindsay J, Corton C, Quail M, Cockfield J, Pathak S, Batra R, Parkhill J, Bentley S, and Edgeworth J. Genome sequence of a recently emerged, highly transmissible multi-anitbiotic- and antiseptic-resistant variant of methicillin-resistant Staphylococcus aureus, sequence type 239 (TW). Journal of Bacteriology 2010 (192) 888-892.] [2 Noto M, Kreiswirth B, Monk A, and Archer G. Gene acquisition at the insertion site for SCCmec, the genomic island conferring methicillin resistance in'' Staphylococcus aureus''. Journal of Bacteriology 2008 (190) 1276-1283.] [3 Osmundson J, Dewell S, and Darst S. RNA-seq reveal differential gene expression in'' Staphylococcus aureus'' with single-nucleotide resolution. PLOS One 2013 (8) 1-12.] [4 ]Yamamoto T, Takano T, Higuchi W, Iwao Y, Singur O, Reva I, Otsuka Y, Nakayashiki T, Mori H, Reva G, Kuznetsov V, and Potapov V. Comparative genomics and drug resistance of a geographic variant of ST239 methicillin-resistant Staphylococcus aureus emerged in Russia. PLOS One 2012 (7) 1-13.